Polychlorinated hydrocarbons, such as carbon tetrachloride, chloroform, trichloroethylene, and tetrachloroethylene have been widely used as chemical intermediates, solvents for dry cleaning of clothing, in degreasing operations, and in a variety of other applications. Chlorinated hydrocarbons are very stable compounds and are relatively toxic at low levels. Groundwaters have become contaminated by chlorinated hydrocarbons from sources such as disposal facilities, chemical spills, and leaking underground storage tanks.
Due to this fact, chlorinated hydrocarbons have been accumulating in the environment, particularly in groundwaters. As a result, pollution of water by chlorinated hydrocarbons as become an important environmental problem and contaminated groundwaters represent a large portion of environmental remedial action plans throughout the world. This is partially due to the improved analytical techniques used for detection of chlorinated hydrocarbons in many water supplies.
It is known that chlorinated compounds can be degraded by reductive dechlorination, that is, replacement of chlorine substituents by hydrogen. Metallic elements, such as iron and zinc, have been used to degrade chlorinated organic compounds.
In the patent literature, patents are issued that use metals or metallic couples to degrade chlorinated organic compounds. In U.S. Pat. No. 3,640,821 to K. H. Sweeney and J. R. Fischer, metallic zinc is used for removing pesticides from aqueous solutions. U.S. Pat. No. 3,737,384, also to Sweeney and Fischer, discloses the use of metallic couples, in solutions buffered to near neutral pH for the degradation of pesticides.
More recently, researchers in Japan have reported on the degradation of 1,1,2,2-tetrachloroethane and trichloroethylene in aqueous solution in the presence of iron powder: Senzaki, T. and Y. Kumagai, "Removal of Chlorinated Organic Compounds from Wastewater by Reduction Process: II. Treatment of Trichloroethylene with Iron Powder" Kogyo Yosui, 1989, 369, 19-25. Gillham and O'Hannesin in their article "Metal-Catalyzed Abiotic Degradation of Halogenated Organic Compounds" IAH Conference on Modern Trends in Hydrogeology: Hamilton, Ontario, May 10-13, 1992, have confirmed Senzaki's results. Recently, Gillham received a U.S. Pat. No. 5,266,213, for his method for cleaning halogenated contaminants from groundwater. The process involves feeding contaminated groundwater through a trench containing a metal such as iron, under strict exclusion of oxygen, and over a lengthy period of time.
The above-mentioned metal systems show the reductive dechlorination of hydrocarbons in aqueous solutions by iron metal. They are disadvantaged in that large amounts of iron are needed for completion of the reactions, as well as, substantial periods of reaction time are required. There is still a need for remediation processes to effectively clean-up aqueous solutions contaminated with chlorinated hydrocarbons.